In the sector of utility vehicles, that is, motor trucks and omnibuses, it is customary to use compressed air braking installations. Vehicles of this type therefore have elements for generating compressed air and for storage, such as, for example, a compressor and a reservoir. The compressor is usually driven by the vehicle engine—permanent and sometimes also releasable couplings, for example via a controllable clutch, being provided between the compressor and the engine.
The proposal to use a compressor as an additional drive unit of a vehicle is disclosed in DE 10 2005 039 281 A1. In this case, it is proposed to operate the existing valves of a compressor, to be precise a high-pressure valve and a low-pressure valve, mechanically via a cam mechanism. In order to change over between the compressor mode and engine mode as operating modes, it is proposed to use a cam phaser, which is known from engine technology. A similar proposal is also disclosed in DE 10 2007 033 693 A1.
However, the use of a cam mechanism with a cam phaser is relatively complicated and costly in mechanical and structural terms. Also, this necessitates a reconstruction of the cylinder head of the compressor.